libphobos: Add Fiber/Thread support for StackGrowsUp.

The StackGrowsDown version being turned off for hppa targets.

After other fixes in the compiler, this allows core.thread unittests to
all pass, as well as the garbage collector to work correctly.

Backported from upstream druntime 2.084.

Reviewed-on: https://github.com/dlang/druntime/pull/2410

From-SVN: r268056

libphobos/libdruntime/core/thread.d

@@ -3254,7 +3254,9 @@ private void* getStackBottom() nothrow @nogc
         pthread_getattr_np(pthread_self(), &attr);
         pthread_attr_getstack(&attr, &addr, &size);
         pthread_attr_destroy(&attr);
-        return addr + size;
+        version (StackGrowsDown)
+            addr += size;
+        return addr;
     }
     else version (FreeBSD)
     {
@@ -3265,7 +3267,9 @@ private void* getStackBottom() nothrow @nogc
         pthread_attr_get_np(pthread_self(), &attr);
         pthread_attr_getstack(&attr, &addr, &size);
         pthread_attr_destroy(&attr);
-        return addr + size;
+        version (StackGrowsDown)
+            addr += size;
+        return addr;
     }
     else version (NetBSD)
     {
@@ -3276,7 +3280,9 @@ private void* getStackBottom() nothrow @nogc
         pthread_attr_get_np(pthread_self(), &attr);
         pthread_attr_getstack(&attr, &addr, &size);
         pthread_attr_destroy(&attr);
-        return addr + size;
+        version (StackGrowsDown)
+            addr += size;
+        return addr;
     }
     else version (Solaris)
     {
@@ -3293,7 +3299,9 @@ private void* getStackBottom() nothrow @nogc
         pthread_getattr_np(pthread_self(), &attr);
         pthread_attr_getstack(&attr, &addr, &size);
         pthread_attr_destroy(&attr);
-        return addr + size;
+        version (StackGrowsDown)
+            addr += size;
+        return addr;
     }
     else
         static assert(false, "Platform not supported.");

libphobos/libdruntime/gc/impl/conservative/gc.d

@@ -30,12 +30,6 @@ module gc.impl.conservative.gc;
 //debug = INVARIANT;            // enable invariants
 //debug = PROFILE_API;          // profile API calls for config.profile > 1
 
-/*************** Configuration *********************/
-
-version = STACKGROWSDOWN;       // growing the stack means subtracting from the stack pointer
-                                // (use for Intel X86 CPUs)
-                                // else growing the stack means adding to the stack pointer
-
 /***************************************************/
 
 import gc.bits;